Lawyers for British-born Ahmed Omar Saeed Sheikh, who is under a death sentence for the murder of the US journalist Daniel Pearl, are planning an appeal based on a confession last week by a top al-Qaida figure.

Sheikh, originally from Wantstead, east London, was sentenced to death in 2002 for the kidnapping and beheading of Pearl, a Wall Street Journal reporter abducted in Pakistan while researching a story on Islamist militants.

But Khalid Sheikh Mohammed - the self-proclaimed mastermind of the attacks on the US of September 11 2001 - said in a confession released by the Pentagon last week that it was he who killed Pearl.

Sheik's lawyer, Rai Basheer Ahmed, who described his client's conviction as "a gross miscarriage of justice", said he planned to make an appeal based on Mohammed's confession.

"In the next court hearing, I am going to submit the recent statement by Khalid Sheikh Mohammed in which he said he himself beheaded the US journalist," Mr Ahmed told Reuters. "From day one, my contention was that the evidence presented in court was not strong enough to lead to the conviction of my client."

Mohammed admitted involvement in more than 30 attacks or plots during a hearing at the Guantanamo Bay prison camp.

"I decapitated with my blessed right hand the head of the American Jew Daniel Pearl," Mohammed said, according to a transcript of his statement.

But intelligence experts are sceptical of Mohammed's confession. Robert Baer, a former CIA field officer assigned to the Middle East, said Mohammed, described as KSM by the US authorities, came across as "boasting, at times mentally unstable".

Writing in Time magazine, Mr Baer said: "I'm told by people involved in the investigation that KSM was present during Wall Street Journal correspondent Danny Pearl's execution but was in fact not the person who killed him. There exists videotape footage of the execution that minimises KSM's role."

Mohammed, 42, a Pakistani brought up in Kuwait, was arrested in Pakistan in March 2003 and handed over to the Americans.

In the transcript Mohammed claimed that Pearl, who had been investigating a trip made by Richard Reid, the would-be shoe-bomber, to Pakistan, had been working for the Israeli intelligence agency Mossad.

Pearl disappeared in the southern Pakistani city of Karachi in January 2002.

The video of the killing, entitled The Slaughter of the Spy-journalist, the Jew Daniel Pearl, shows a man cutting Pearl's head off. His severed head is then held up by the hair. In the transcript Mohammed says: "For those who would like to confirm, there are pictures of me on the internet holding his head."

Sheikh, who attended the private Forest school in Snaresbrook, east London and who dropped out of the London School of Economics, was sentenced to death while three co-accused were jailed for life.

The convicts appealed to the Sindh provincial high court in July 2002. The government also appealed to the same court, asking for more severe penalties for the co-accused.

But court hearings have been repeatedly postponed, mostly because of the absence of lawyers representing the convicts. Under Pakistani law, a convict has the right to appeal in superior courts but no case can be heard if lawyers of the convict are absent.